apps: fix substitution issue by generating k8s kustomizations

apps/do/kustomization.yaml

 apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 resources:
-  - vikunja-kustomization.yaml
   - vikunja-secrets-kustomization.yaml
+  - vikunja-kustomization.yaml

apps/forge/kustomization.yaml

+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - forgejo-kustomization.yaml
+  - forgejo-secrets-kustomization.yaml

apps/generate-kustomizations.sh

 #!/bin/sh -e
-# Generates kubernetes kustomizations
+# Generates kubernetes kustomizations for given directories or all subdirectories
 if test $# -gt 0
-then dir=$1
+then for dir; do
 	{ echo 'apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 resources:'
 	find $dir -maxdepth 1 -type f -name "*.yaml" -not -name "kustomization.yaml" -printf "  - %f\n"; } | tee $dir/kustomization.yaml
+	done
 else
 	find -mindepth 1 -maxdepth 1 -type d | while read dir
-		do echo "$dir"
+		do echo "$dir"
 			$0 "$dir"
 		done
 fi

apps/ninja/kustomization.yaml

+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - invoiceninja-kustomization.yaml
+  - invoiceninja-secrets-kustomization.yaml